An internal combustion engine for a vehicle may operate in variety of combustion modes. One example mode is spark ignition (SI), where a spark performed by a sparking device is used to initiate combustion of an air and fuel mixture. Another example mode is homogeneous charge compression ignition (HCCI), where an air and fuel mixture achieves a temperature where autoignition occurs without requiring a spark from a sparking device. In some conditions, HCCI may have greater fuel efficiency and reduced NOx production compared to SI. However, in some conditions, such as with high or low engine loads, it may be difficult to achieve reliable HCCI combustion.
One approach includes operating the internal combustion engine using SI during some conditions and HCCI during other conditions where advantageous. In this manner, the engine can be configured to transition between HCCI operation and SI operation based on engine load, for example, so that a transition can be performed to SI operation when the engine load is lower or higher than the range where reliable HCCI operation can be achieved.
The inventor herein has recognized a disadvantage with such an approach. Specifically, transitions between HCCI and SI may be inefficient and/or difficult to achieve under some conditions. Thus, in some examples, reducing these transitions may serve to increase efficiency and/or reduce the apparent deficiencies in engine control.
One approach to overcoming the above disadvantage may include a method of operating an engine having a plurality of combustion cylinders configured to produce an engine output, comprising: adjusting a condition of the engine to achieve combustion by each of spark ignition and homogeneous charge compression ignition; and varying the engine output by at least varying a number of cylinders carrying out combustion.
In another approach described in U.S. Publication No. 2005/0173169, a dual combustion mode engine configured in a hybrid vehicle propulsion system is used, wherein the engine is configured to operate in HCCI mode under some conditions and SI mode under other conditions. In this manner, the hybrid system may be used to reduce transitions between combustion modes while maintaining the requested output to the vehicle drive wheels.
The inventor herein has likewise recognized disadvantages with the approach of U.S. Publication No. 2005/0173169. For example, limits on the operating range of HCCI operation in combination with the resulting transitions to SI operation caused by such limits, may reduce engine efficiency and drive feel.
Thus, the interrelation of these issues may exacerbate transitions and result in increased fuel consumption outside the limits of HCCI operation more than necessary.
These limitations may be addressed in some examples by a method for controlling a vehicle propulsion system having an engine configured to produce an engine torque configured to propel at least a drive wheel, wherein the engine includes a plurality of cylinders; a motor configured to selectively supply a motor torque to at least said drive wheel; and a generator coupled to the engine, wherein the generator is configured to selectively absorb at least said engine torque, the method, comprising during vehicle propulsion system operation, selectively varying at least each of: a number of cylinders carrying out combustion; a combustion mode of at least one cylinder carrying out combustion between at least a spark ignition combustion mode and a homogeneous charge compression ignition combustion mode; a motor torque supplied by the motor; and an engine torque absorbed by the generator.
In this manner, by recognizing that transitions between combustion modes can be reduced and improved engine operation can achieved by deactivation of certain cylinders rather than requiring transitions to less efficient operating modes, the combination of a multiple combustion mode engine utilizing cylinder deactivation with a hybrid propulsion system can thereby reduce transitions between combustion modes and improve overall hybrid vehicle operation.